1. Field of the Invention
The present invention relates to an injection pressure control apparatus for a die cast machine and an injection mold machine, and in more detail, an apparatus for controlling whether the operational status of the oil pressure circuit of an injection device is proper.
2. Description of the Related Art
In a die cast machine, an injection has been carried out in such a manner that an injection plunger drive speed is changed from low to high by the function of a pressure increase circuit when injecting the molten metal in the mold cavity, to avoid enfolding air into the molten metal filled in the injection sleeve. It is also necessary to control the injection pressure precisely as a factor in making the quality of the die cast products stable. Accordingly, it is quite important to check the state of this injection pressure in order to produce die cast products having superior quality while avoiding many defective products.
In order to check the state of the injection pressure, the operational state of the pressure increase circuit can be monitored, for instance, to detect the pressure change condition of an oil pressure circuit.
However, in the conventional die cast machine, since no such pressure measuring apparatus which can detect the pressure change condition mentioned above is provided, it is not possible to detect the change in the oil pressure control state of an injection cylinder when the oil pressure circuit comes into the abnormal state.
Accordingly, it has been impossible to avoid the problem of manufacturing many defective products, when the abnormal state is generated.
Further, the injection pressure through the process of injection by the injection mold machine is normally maintained at a low value at first, but gradually increases proportionably as the mold cavity is filled with molten resin. Accordingly, in the normal operation of the injection mold machine the increasing change of pressure constantly appears.
However, in a multi-cavity mold or multi-gate mold, if some of the gates are clogged up, the flowing velocity of the molten resin which runs through the remaining gates increases to generate an excessive pressure which causes defective moldings.
Therefore, in the injection mold machine, important for manufacturing moldings of a stable quality, it is important to detect and maintain the proper injection pressure.